This invention relates to a method and system for applying a stimulating current flow to core samples taken from subterranean formations and relates more particularly to a method and system for regulating the stimulating current flow through core samples having non-linear properties.
In the drilling of wells, such as oil or gas wells, cores are taken of the earth strata through which the wells are drilled and various characteristics of the cores or core samples are determined for the purpose of establishing fluid in the strata, estimating the quantity of fluid in the strata, the ease of flow through the strata, etc. Such core samples are also taken from producing strata and characteristics of the core samples are determined for the purpose of estimating fluid reserves, predicting production rates, etc. Among the characteristics of core samples commonly determined is the formation resistivity factor involving the measurement of the electrical resistivity of the core samples.
However, previous methods for measuring electrical resistivity of core samples have failed to take into account certain factors which affect the resistivity measurements. It has been found that core samples of earth material may exhibit nonlinear properties. When a core sample with such non-linear properties is stimulated with a sine wave its response is distorted from a sine wave response. This distorted response is due to the fact that at some current density there is a threshold for inducing an electro-chemical reaction. It is therefore an object of the present invention to overcome such a non-linearity factor in the measurement of the electrical resistivity of core samples.